The invention is directed to N-silylpropyl-N'-acyl-ureas, a process of their production and the setting free of the blocked isocyanate function.
Silanes of the general structure I have large scale significance as coupling agents in material systems which consist of an inorganic and an organic phase, as well as for the modification of OH functional surfaces: EQU (R.sup.4 O).sub.3 Si--CH.sub.2 --CH.sub.2 --CH.sub.2 --X (I)
(R.sup.4 =CH.sub.3, C.sub.2 H.sub.5)
The most important functional groups include: X=NH.sub.2, --S.sub.4 -- (Si 69), --SH, --Cl, --O--CO--C(CH.sub.3).dbd.CH.sub.2 and ##STR1##
The isocyanate function (X=--NCO) represents a particularly valuable functional group:
On the one hand it can be reacted with numerous H-acidic, monomeric materials (amines, alcohols, oximes, and many others) with the formation of newer functional silanes, on the other hand it can also react with polymeric resins and rubbers in mutual binding. In contrast to the advantage of the multifold chemical activity there is the disadvantage of the high toxicity of the isocyanate group and the cumbersome synthesis of the silane (II) in practice (Hedaya U.S. Pat. No. 4,130,576): EQU (R.sup.4 O).sub.3 Si--C.sub.3 H.sub.6 --NCO (II)
In industry therefore there are frequently employed blocked alkyl and aryl isocyanates: (Z. W. Wicks, Progr. Org. Coat. Volume 9, (1981) pages 3-28.
As blocking agents for the non-silyl containing organic isocyanates there are used, e.g. alcohols (especially phenols), .beta.-dicarbonyl compounds, lactams or oximes. Blocked isocyanates on the one hand are usable from aqueous systems and on the other hand relatively inexpensive procedures are sufficient for safely handling them because of their comparatively low toxicity.
In Berger U.S. Pat. No. 3,994,951 there is described a hydrolyzable silane from which the isocyanate function is set free at a temperature of 160.degree. C. which silane is O-methyl-N-trimethoxysilyl-propyl-urethane.
This compound, however, is little suited for use as an coupling agent in filler reinforced polymer systems for the reason that the thermolysis only proceeds at relatively high temperatures and the byproduct methanol (flash point: 11.degree. C.) formed makes it necessary to take corresponding safety precautions.
The thermolysis of O-methyl-N-trimethoxysilylpropyl urethane can only be carried out in good yields if there is used very slow thermolysis. The cause of this must be that the thermolysis byproduct methanol is more volatile than the desired 3-isocyanatopropyltrimethoxysilane, so that in the distillative separation of the latter silane from the thermolysis sump the recombination of methanol and 3-isocyantopropyltrimethoxysilane in the gas phase can only be prevented if this separation is carried out comparatively slowly. The thus attainable time-space yields are unsatisfactory for an industrial process.
The same is true for the process for the production of 3-isocyanatopropylsilanes by gas phase esterification of 3-isocyanatopropyltrichlorosilane with alcohols (Bennett U.S. Pat. No. 3,651,117) in which the simultaneously undesired side reaction of the isocyanate group with the alcohol can be suppressed only through an industrially expensive procedure.
The invention is directed to hydrolyzable silanes having a blocked isocyanate function and a process for their direct production in high yields.
Simultaneously the isocyanate group should quite easily be set free by thermolysis.